At present, image display devices which office automation equipment such as a television set and a desktop personal computer include are shifted from a hitherto predominant CRT to a liquid crystal display having large advantages of low-profile and lightweight design and low power consumption. Applications of the liquid crystal display are widely spread not only to television sets and desktop personal computers but also to onboard navigation systems, instruments for use indoors and outdoors and the like. Liquid crystal displays currently becoming widespread have polarizers having functions to transmit and shield light and retardation films including a liquid crystal layer having a photonic switching function as elementary components, and in addition a hard coated layer for protecting a surface, an antireflection film and the like are added.
When the polarizer is fabricated, a polarizing film is first fabricated generally by stretching (uniaxial stretching) a polyvinyl alcohol-based film which has been swelled, then dyeing (or uniaxially stretching after or during dyeing) and fixing a dyeing agent with a borate compound. And, by bonding a protective film such as a triacetyl cellulose film to the fabricated polarizing film, the polarizer is fabricated. In addition, the above-mentioned dyeing and fixing may be simultaneously applied. Further, the above-mentioned stretching includes wet stretching in which stretching is carried out in a liquid and dry stretching in which stretching is carried out in a gas.
Here, color irregularities produced because of existence of variations in optical properties over the whole area of the polarizing film are often present in the polarizing film. As a specific reason why these color irregularities occur, various factors are thought, but it is difficult to ascertain the reason unless the polarizing film is in a state of bonding a protective film such as a triacetyl cellulose film to the polarizing film. When a defect of quality due to color irregularities of the polarizing film is observed in a state of bonding a protective film, the polarizing film is discarded as defectives together with the protective film, and therefore the yield of a material will be largely deteriorated.
As a method of improving these color irregularities, for example, in Japanese Unexamined Patent Publication No. 2004-78208, there is proposed a method in which the length of a dyeing bath in which dyeing is carried out is changed and a dyeing time is controlled, and this allows the dyeing irregularities of the polarizing film to decrease.
However, polarizing films having a large area are required in large amounts with the upsizing of the liquid crystal display in recent years. When an area of the polarizing film becomes large, the evenness of optical properties over the whole area of the polarizing film is required or a combined use with another films such as a retardation film which corrects an angle of view becomes often, and therefore the problem of color irregularities becomes significant and a requirement for fabricating the films in a short time (short delivery times) is increasing. If a current processing speed of the overall manufacturing process is increased in respond to the requirement for fabricating the films in a short time, there are problems that color irregularities are apt to occur and its yield is largely deteriorated. On the other hand, in accordance with the method described in the above-mentioned Unexamined Patent Publications, the color irregularities can be reduced as described above, but it is necessary to extend considerably a dyeing time by decreasing a carrying speed of the polarizing film or lengthening the length of a dyeing bath in order to respond to the polarizing film having a large area, and there is a problem that the requirement of fabricating the polarizing films in a short time cannot be met.